New @lde/distribution-health leaf: validity verdicts + usability rollup

[ddeboer]

Part of the distribution-health feature: netwerk-digitaal-erfgoed/dataset-register#2103 (reachability + validity → usability).

New leaf package @lde/distribution-health, depending on @lde/distribution-probe. Deliberately acyclic: it interprets the prober’s raw results; the prober does not produce verdicts.

Modules (all pure)

• validity-verdict type + reasons (parse-error, empty), carrying a best-effort parser message, the validatedFingerprint, and producer depth.
• probe-result → verdict mapper (shallow) and import-outcome → verdict mapper (deep).
• usability rollup: (reachability, validity verdict(s), current fingerprint) → { usable | unusable | unknown, cause }.
  • Precedence: unavailable ⇒ unusable; reachable + false ⇒ unusable; reachable + true ⇒ usable; reachable + none/stale ⇒ unknown.
  • Staleness gate: a verdict applies only if validatedFingerprint equals the current fingerprint, else it decays to unknown.
  • Depth preference: a deep verdict wins over a shallow one.
• validity → DQV/PROV quads mapping.

Tests

External-behavior (input → output) tests on the three pure modules; an exhaustive case matrix for the rollup (reachability × validity × fingerprint-fresh/stale × depth). Prior art: sourceFingerprint.test.ts, report.test.ts.

Vocabulary lands in definitions; the normative usability rule is specified in the PRD (netwerk-digitaal-erfgoed/dataset-register#2103).